var apiFileLineRegexp = regexp.MustCompile(`^pkg ([^ \t]+)[ \t]*(\([^)]+\))?, ([^#]*)(#\d+)?$`)

// parseAPIFile parses a file in the api format and returns a list of the file's features.
// A feature is represented by a single line that looks like
//
//	pkg PKG (BUILD) FEATURE #ISSUE
//
// where the BUILD and ISSUE may be absent.
func parseAPIFile(fsys fs.FS, filename string) ([]APIFeature, error) {
	f, err := fsys.Open(filename)